1. Field of the Invention
This invention relates to the field of conifer growth stimulation and forest management methods and compositions useful in such methods.
2. Description of the Art
Forest resource preservation and development becomes increasingly difficult as societies become more industrialized and affluent. The more developed the culture, the more destructive it becomes of its forests due to man-made calamities such as forest fires and to the consumption of forest products such as lumber and pulp. Paradoxically, expanding, affluent populations also demand more recreational areas for enjoyment of increased leisure time. Unfortunately, these conflicting demands occur at a time when the choicest, most productive soils are employed for agriculture or are occupied by industrial or residential structures. Consequently, silviculture is generally confined to remote areas in which soils are typically deficient in major and minor nutrients required for abundant plant growth.
Efforts to improve forest growth and maximize productivity have involved fertilization with either solid fertilizers or aqueous fertilizer solutions. Fertilization with solid nutrients usually involves application of urea, ammonium nitrate or other nitrogen source as relatively large solid prills of sufficient size to penetrate the forest canopy and reach the ground surface. A majority of nitrogen applied in this manner usually escapes by leaching or volatilization unless the nutrient is promptly washed into the soil and converted to nitrates (in the case of urea). Consequently, such practice is usually employed only during the rainy season and, thus, is logistically inefficient due to the intensity of effort required for wide spread fertilization in the few rainy months. Such practice also causes maximum ecological disruption since the fertilizer is applied at the time when it is most likely to contaminate forest streams and lakes. The use of solid fertilizer in this manner is inefficient for the further reason that much of the applied nitrogen is rapidly assimilated by shallow-rooted undergrowth such as ferns and broadleaf vegetation. More efficient foliar fertilization methods are described in my U.S. Pat. No. 4,033,747 for Silvicultural Fertilization and involve the application of concentrated nitrogen solutions directly to the forest canopy.
The presence of undesired vegetation such as ferns, weeds, and broadleaf trees and plants further complicates conifer forest management even in the absence of fertilization since such plants compete with conifer trees for nutrients and impair access to forested areas. Competition for nutrients, sunlight and water is particularly detrimental to conifer growth in reforested areas since broadleaf trees and underbrush typically grow much faster in their earlier stages of development than do conifer seedlings. Thus, broadleaf plants and other undergrowth can completely crowd out small conifer seedlings or markedly impair their growth rate unless the non-conifer species are controlled by mechanical or chemical thinning. One method for simultaneously fertilizing conifers and eliminating competing non-conifer growth is disclosed in U.S. Pat. No. 4,035,173 of S. Hashimoto and Donald C. Young, Selectively Thinning and Fertilizing Timber Forests, the disclosure of which is incorporated herein by reference in its entirety. That patent teaches, in part, that broadleaf plants can be selectively eliminated from preferred conifer trees by applying to the foliage of all plants an aqueous solution of a water-soluble nitrogen source having a nitrogen concentration corresponding to at least about 12.5 weight percent elemental nitrogen at a nitrogen dosage rate sufficient to kill a significant proportion of the broadleaf plants. Other chemical thinning methods usually involve herbicide application by ground personnel or vehicles, both of which are tedious, time consuming and expensive, as is mechanical thinning by ground personnel. Yet such procedures are sufficiently productive to justify their use. Mechanical clearing of undesired vegetation is sometimes practiced even as late as 15 years after planting and typically involves substantial costs on the order of $100.00 to more than $500.00 per acre. Yet the United States Forest Service has established that ultimate wood protection can be increased sufficiently to justify such practices.
Biuret is known to be highly phytotoxic to essentially all plant varieties when applied in a manner which provides direct contact with either plant foliage or roots. Biuret applied to the soil of deep rooted plants is generally less toxic since it is only slightly soluble in water (less than 2 weight percent at 25.degree. C.) and is generally degraded in the soil before it can be assimilated by the plant. However, application of biuret directly to plant foliage or to shallow rooted plants, such as young seedlings, is known to produce dramatic phytotoxic response and often results in plant stunting or death. Many authorities flatly state that the biuret content of foliarly applied urea should not exceed 0.25 weight percent. See, for instance, the "Farm Chemicals Handbook," Meister Publishing Company., Willoughby, Ohio, 1981 under "Urea" and "LB Urea", and the "Western Fertilizer Handbook", 5th. Ed. Interstate Printers and Publishers, Inc., Danville, Ill., 1972, page 163. Paradoxically, biuret is often formed during the manufacture of urea, especially prilled urea--one of the most widely used nitrogen fertilizers. For that reason, various safeguards are built into modern urea manufacturing facilities to prevent biuret production, and various procedures have been devised for removing biuret from urea. Illustrative biuret-removal methods are discussed by Donald C. Young and James A. Green, II in Ser. No. 753,692 filed July 10, 1985 for Methods for Removing Biuret from Urea by Adsorption, now U.S. Pat. No. 4,701,555, Ser. No. 753,693 filed July 10, 1985 for Biuret Purification, now U.S. Pat. No. 4,698,443, Ser. No. 732,175 filed May 7, 1985 for Biuret Manufacture, now U.S. Pat. No. 4,645,860, Ser. No. 725,304 filed Apr. 19, 1985 for Methods for Purifying Biuret, now U.S. Pat. No. 4,645,859, Ser. No. 567,271 filed Dec. 30, 1983 for Methods for Removing Biuret from Urea by Ion Exchange, now U.S. Pat. No. 4,658,059, Ser. No. 567,099 filed Dec. 30, 1983 for Ion Exchange Methods for Removing Biuret from Urea, now U.S. Pat. No. 4,650,901 and Ser. No. 567,047, filed Dec. 30, 1983 for Methods for Removing Biuret from Urea, now U.S. Pat. No. 4,654,442 the disclosures of which are incorporated herein by reference in their entireties.